Revert "radix tree test suite: fix compilation"

This reverts commit 53855d10f4.

It shouldn't have come in yet - it depends on the changes in linux-next
that will come in during the next merge window.  As Matthew Wilcox says,
the test suite is broken with the current state without the revert.

Requested-by: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/radix-tree.c

@@ -30,6 +30,7 @@
 #include <linux/percpu.h>
 #include <linux/slab.h>
 #include <linux/kmemleak.h>
+#include <linux/notifier.h>
 #include <linux/cpu.h>
 #include <linux/string.h>
 #include <linux/bitops.h>